Structure and bonding analysis of dihalogallyl and dimethylgallyl complexes of molybdenum and tungsten [(η5-C5H5)(CO)3M(GaX2)] (M = Mo, W; X = Cl, Br, I, Me): A theoretical study

The electronic, molecular structures and bonding of the terminal neutral dihalogallyl and dimethylgallyl complexes of molybdenum and tungsten [(η5-C5H5)(CO)3M(GaX2)] (M = Mo, W; X = Cl, Br, I, Me) were investigated at the DFT/BP86/TZ2P/ZORA level of theory. The calculated geometry of molybdenum complex [(η5-C5H5)(CO)3Mo(GaMe2)] is in excellent agreement with structurally characterized complex [(η5-C5H5)(CO)3Mo(GatBu2)]. The Pauling bond order of the optimized structures shows that the M–Ga bonds in these complexes are nearly M–Ga single bond. The gallium bound substituent exerts an influence on the length of the M–Ga bonds. The M–Ga bond distances are longer for dimethylgallyl complexes than the dihalogallyl complexes. The Mayer bond order of the M–Ga bonds decrease on going from X = Cl to Me, indicating progressive weakening of the M–Ga bond. The M–Ga σ bonding orbitals are significantly polarized towards the metal atom. The π-bonding component of the total orbital contributions is significantly smaller than that of σ-bonding. Thus, in these complexes the GaX2 ligand behaves predominantly as a σ-donor. Orbital contributions for the interactions between neutral fragments [(η5-C5H5)(CO)3M] and [GaX2] are larger while the electrostatic interactions, interaction energies and bond dissociation energies are significantly smaller than the values obtained for the interactions between ionic fragments [(η5-C5H5)(CO)3M]+ and [GaX2]−. The Ga–C(CO) bond distances are smaller than the sum of van der Waal radii (Ga–C(CO) = 2.60 Å) and thus, suggest the presence of weak inter-molecular Ga–C(CO) interactions.